It is a common goal within the motor industry to reduce the weight of vehicles in order to permit more fuel-efficient engines to be used, while at the same time maintaining acceptable performance standards.
The majority of passenger vehicles currently in production have bodies which are manufactured from steel. Steel is an attractive material since it is relatively easy to form into complicated shapes, and components and panels made of such material can be easily joined by welding. In addition, pressed steel panels can be painted to provide an excellent surface finish. The ability to shape and join steel components implies that a vehicle body can be designed to provide the desired degree of stiffness and, importantly, progressive collapsibility in the vent of an accident. A major disadvantage with still is, however, its weight.
As an alternative to steel, aluminum has been used in certain vehicle body constructions for many years, primarily as low stressed body panels. More recently, vehicles have been produced comprising a space frame of interconnected aluminum members to which aluminum panels are attached. Aluminum, however, suffers from the disadvantages that it is relatively difficult to join together and that it is comparatively expensive.
Vehicle bodies made from composite materials such as glass fiber reinforced plastic are well know. These composite bodies have a low stress-bearing capability and vehicles equipped with such a body must therefore also employ a chassis which supports the running gear.
A stress-bearing composite structure for use as a vehicle platform is described in Swedish Patent No. 326,894. The structure is said to consist of a closed hollow body made up of a pair of joined-together shells, with the body being filled with a hard foamed plastic. In order to impart sufficient strength to the structure in desired regions, the density of the foamed plastic is increased.
A composite chassis subframe structure is disclosed in European Patent No. 594,131 in which a foam core is sandwiched between reinforcing fiber preforms and is further wrapped with additional reinforcing fiber cloth. Steel inserts for attaching suspension and other chassis components are also wrapped and retained to the foam core. The sandwiched and wrapped foam core is then placed in a mold and plastic resin is injected, thereby impregnating the fibers.
Magnesium has been used for many years in the automobile industry, particularly for small components, though until recently its light-weight advantages were offset by the inability to overcome its susceptibility to corrosion.
In order to rationalize production of motor vehicles, it is highly desirable to be able to make use of standardized components, i.e. as many common components as possible are used in different models.
In view of the above, the present inventor has identified a need for a stress-bearing assembly which can be used in vehicle body constructions which is lighter than conventional assemblies while at the same time still providing adequate stiffness, and which assembly may easily be adapted to different models of vehicles.